1. Field of the Invention
This invention relates to a new process for the catalytic hydrogenation of fatty acid methyl esters using particulate and/or granulated catalysts containing copper chromite under pressures in the range from 20 to 100 bar.
2. Description of Related Art
Fatty alcohols, i.e., predominantly linear, monofunctional alcohols having chain lengths of 8 and more carbon atoms, and their production are described in detail in the literature, for example, in Ullmanns Encyklopaedie der technischen Chemie, 4th Edition, Vol. 11, pages 427 to 445. A preferred starting material for their production are the fatty acids and fatty acid mixtures occurring in natural fats and/or oils which may be converted into fatty alcohols of corresponding chain length by catalytic hydrogenation. Through the use of the fatty acids to be reduced in the form of their methyl esters, the catalysts in particular are protected against aggressive attack by the free carboxyl group, so that industrial processes can be operated for sufficiently long periods with satisfactory volume-time yields. Today, therefore, the predominant quantity of native fatty alcohols is produced from fatty acid methyl esters by the gas-phase hydrogenation process in which the distilled methyl esters are passed in the vapor phase, together with a large excess of hydrogen, over a fixed bed of copper-containing mixed oxide catalysts, such as, for example, copper chromite spinel catalysts, at temperatures above 200.degree. C. and under pressures of from about 250 to 300 bar.
The copper-mixed oxide catalysts obtained by co-precipitation via the wet route are used as particulate catalysts or extrudates and, before use, are generally reduced in the plant or installation.
According to the relevant patent literature, fatty acid esters, more especially fatty acid methyl esters, and free fatty acids are therefore simultaneously used as starting materials for the hydrogenation reaction to saturated and/or unsaturated fatty alcohols, for example, as described in German Patent Publications DE-PSS 965 236, 10 05 497, 25 13 377 and 26 13 226. U.S. Pat. Nos. 4,113,662, 4,482,766, and 4,199,479 as well as Indian Patent 124510 also describe pertinent process features. As far as industrial application is concerned, the proposals mentioned have to be evaluated entirely differently according to whether the fatty acid esters or the free fatty acids are used as starting material for the hydrogenation.
German Patent Publication DE-OS 34 25 758 describes a process for the production of alcohols, more particularly either furfuryl alcohol by hydrogenation of furfural or fatty alcohol by hydrogenation of fatty acids containing a corresponding number of carbon atoms or esters thereof under a pressure in the range from 20 to 100 bar. The process is carried out at a temperature in the range from 150.degree. to 300.degree. C. and in the presence of a catalyst containing a mixture of copper and chromium on the one hand and copper on a support on the other hand. Under the described conditions, reduction of the fatty alcohols to the corresponding hydrocarbons is also observed in practice thereby jeopardizing the economy of the process through a reduction in yield. Another disadvantage is the fact that the catalysts used in the prior processes show inadequate mechanical strength. The solid catalyst is extremely difficult to separate from the reaction products and this causes losses of active catalyst through washing away of catalyst material.